The release mechanism for core release machines that comprised the subject matter of Spanish patent application No. 8703409 corresponding to U.S. application Ser. No. 079,034, of the same applicant, has a bearing that can move toward the blowing cartridge, i.e, toward the cartridge containing the sand to be inserted in a core box. To such end said bearing is provided with two hollow guide-columns playing inside respective bushings, to which they are coupled closely, such bushings in turn extending into conduits connecting them to a small tank that supplies jet air, a release valve being provided in the bearing to allow discharge of the tank pressure towards the cartridge once the bearing has been duly coupled to such cartridge.
The purpose of said guide-columns is obviously to allow the bearing to retract or rise to facilitate sand substitution in the cartridge and subsequent displacement of the bearing toward the cartridge in order to tightly close the latter, at the stage when the jet air is released.
The above functions are carried out in said Spanish patent application with the assistance of a hydraulic cylinder ensuring efficient operation of the work cycles of the release mechanism.
However, it just to happens that when the core box is large and therefore has a large surface, once jet air has been released, there is a strong back pressure driving the blowing head, i.e., the said bearing, upwards, and the pressure inside the hydraulic cylinder is not enough to balance the said drive.
This results in an inadequate compacting of the cores, as a consequence of the pressure loss and an unwanted air leak dragging sand.
Thus, as a consequence of the back pressure ensuing on instantaneous jet air release, the tight coupling between the blowing head and the cartridge is broken, in given cases.
Although this problem does not arise when the core boxes are small on their closure is vertical, where the back pressure problem is negligible, this problem becomes important in the aforesaid cases, where the core box has a large surface.